The invention relates to a correction method for a magnetic field probe by which an external magnetic field, particularly the earth's magnetic field, is respectively measured in terms of strength and direction. Moreover, the invention relates to a device for the implementation of this method.
Magnetic field probes such as electronic compasses are already known in various forms. For example, such probes are constructed with two coils which are perpendicular relative to one another and whose induction is influenced by the earth's magnetic field or by some other external magnetic field. Measuring methods which exploit this effect are disclosed, for example, in the German patent application Nos. P 29 49 815; P 30 29 532; and P 31 21 234; all incorporated herein by reference.
In the employment of compasses, particularly in vehicles such as in ships, aircraft, and even land vehicles, various errors occur which become apparent as a result of a magnetic declination. This magnetic declination arises, on the one hand, as a result of undesired magnetic fields in the vehicle or in the probe itself and, on the other hand, as a result of the probe not having been operatively positioned in an exactly horizontal fashion. A further error can result from the type of probe. If, for example, the two components of the magnetic field are measured in the probe with two different coils, then errors can result from inequalities of the two coils or in the evaluation electronics.
In order to avoid magnetic declinations in compasses, it is already known to slowly rotate the vehicle with the built-in compass by 360.degree. on a compensation platform. Accordingly a data table is produced point-by-point from which the allocation between the indicated and true angle relative to magnetic North results. Another possibility of correction consists in reducing the magnetic declination with the assistance of individually attached compensation magnets. The execution of these techniques is involved. In particular, they are difficult to automate or they lead to high apparatus expense.